What is Low Level Laser / Light Therapy (LLLT)? Treatment and cosmetic indications

Low Level Laser (or light) Therapy or LLLT is a type of treatment that employs light emitting sources to modulate cellular activity. It was discovered in the 1960s, but in the last 20 years it has been extensively investigated for a wide range of applications from reducing pain and inflammation, to stimulate wound and tissue healing and, in the field of cosmetic dermatology, to fight hair loss, rejuvenate the skin, control acne, and treat scars among the many.

photobiomodulation (PBM) or low level laser therapy (LLLT)

What is LLLT treatment?

Low level light therapy, also known as photobiomodulation (PBM), photomodulation, or biolight therapy, is a treatment that uses LEDs (light emitting diodes) or low-level laser light to stimulate cells in order to produce beneficial effects for the patients.

While doctors and scientists have focused on UV light for decades in the past, it is now clear that visible light has a great impact on our skin in particular and on our organism in general: from inducing free radicals formation, to pigmentary changes in the skin like melasma and post-inflammatory hyperpigmentation, to erythema and other skin pathologies, visible light has a role in all of these and more. The greater wavelength of visible light makes it a “lower energy” source, but it increases its penetration when compared to higher energy sources like UVs: UVBs for example are capable of penetrating only the epidermis layer of the skin, while UVA can reach the dermis layer; visible light instead, and in particular red and near infrared light, can penetrate the skin up to the subcutaneous adipose layer in the hypodermis.

human skin diagram
By Tomáš Kebert & umimeto.org – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=93271515

How does low level laser therapy work?

When talking about light-based devices, such as lasers and IPL, these can work due to one of the two following principles:

  1. Photothermal interaction: the light from the device is absorbed by a target tissue and transformed into heat, causing its destruction (coagulation/vaporization). E.G.: Carbon Dioxide lasers (CO2 lasers).
  2. Photomechanical interaction: the light from the device causes a shockwave effect due to the high energy release which in turn causes the fragmentation of the tissue. E.G.: Q-Switched lasers and Picosecond lasers.

The photobiomodulation therapy instead works following a completely different principle: photochemical interaction. The light, in this case, activates chemical reactions which produce an effect on the cells, tissues and/or organism, without generating heat, damage or destruction of the cell or tissue.

In the field of cosmetic dermatology, low level laser therapy works by stimulating fibroblast proliferation, collagen synthesis, growth factors and extracellular matrix production, and improving the circulation in the skin by stimulating angiogenesis (building new blood vessels) and increasing the blood flow. In general, LLLT seems to produce a wide range of effects on the cells and tissues, like increasing ATP (energy) production in the cells and transcription factors which are responsible for turning ON and OFF genes, transcribing DNA into RNA and ultimately synthetize proteins which are fundamental for the function of the cell., but I won’t get too much into details on their mechanism of action for simplicity, the important thing to note is:

  1. Visible light and LLLT devices do have an effect on cells and tissues.
  2. The working principle is completely different from other light-based devices like lasers and IPL.

Moreover, low level light therapy also seems to produce a wide effect on the organism, not just on the area irradiated by light: in trials for wound healing, skin rejuvenation or acne where only a portion of the skin (half face or only one wound) was treated, the effects were not limited to the treatment area but were seen also, at least to some extent, in the untreated areas. This did not happen with sham control.

Different colors and benefits of photobiomodulation therapy

Molecules have different chromophores, which are the part of the molecule that absorbs a specific wavelength of light, giving it color. For this reason, some molecules with certain chromophores may react to a particular wavelength (colored light) and not to others and therefore different wavelengths produce different effects on cells and tissues and have different characteristics as well.

human visible spectrum of light
Horst Frank, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Blue light for LLLT

Light falls in the blue spectrum when its wavelength is around 400-470 nm; in this range, blue light is UV-free and safe to use. At 400 nm the light penetrates less than 1 mm of skin and is therefore suitable for treating only superficial conditions such as targeting the bacteria responsible for acne (Propionibacterium acnes).

Green light for LLLT

Light falls in the green spectrum when its wavelength is around 470-550 nm. Green LLLT is currently being researched both in-vitro and in-vivo in animal studies and it’s showing potential in the treatment of several conditions, sometimes having a greater effect than red light on cells and tissues.

Yellow light for LLLT

Light falls in the yellow spectrum when its wavelength is around 590 nm. Yellow light is highly absorbed by blood, making yellow light therapy a potential treatment for superficial vascular skin conditions like rosacea. This and other potential applications have yet to be investigated and yellow LLLT has no clinical indication yet.

Red light for LLLT

Light falls in the red spectrum when its wavelength is around 630-700 nm. Red LLLT has many indications in multiple fields of medicine and has been researched extensively. Besides its use in cosmetic dermatology, red LLLT is also employed in photodynamic therapy (PDT) to activate other drugs and treat some forms of skin cancer.

Near-infrared (NIR) light for LLLT

Light falls in the NIR spectrum when its wavelength is around 700-1200 nm. NIR LLLT covers most of the applications for this type of therapy, from pain relief to skin rejuvenation, wound healing and hair restoration. NIR light also has the greatest penetration in the skin, delivering the treatment deep into the hypodermis.

Current applications of photobiomodulation in cosmetic dermatology and aesthetic medicine

LLLT has multiple applications in the field of aesthetic medicine and cosmetic dermatology, here below I’ll briefly go over the most common ones.

Low level laser therapy for hair regrowth

LLLT seems to be an effective treatment for androgenetic alopecia, leading to improved hair density and increased hair thickness. The wavelength employed for this purpose are generally around 630-660 nm (red light) and generally 3 sessions per week, 20 minutes each, are suggested to fight hair loss.

LLLT for Skin Rejuvenation: Wrinkles and photoaging

Skin rejuvenation is one of the most investigated applications for LLLT. In studies, the most commonly used wavelength was 570-850 nm (ranging from red to near-infrared) and the treatment protocol varied between once a day sessions to 2 or 3 sessions per week, for 20-30 minutes each session.

There is clear evidence of increased growth factors release, increased number of fibroblasts and increased fibroblast activity which results in increased collagen and elastin production, extracellular matrix regeneration and ultimately in reduced wrinkles and increased skin elasticity.

Treatment does not seem to lead to long lasting results: while the improvements may be noticeable up to 12 weeks after the last session, it seems like a continued use and a maintainance protocol may be advisable for noticeable and long-lasting results.

Pigmentation issues: LLLT for melasma and post-inflammatory hyperpigmentation (PIH)

Near-infrared and infrared light seems to downregulate melanin synthesis. LLLT has shown some effectiveness in treating melasma and PIH as well as treating other pigmentation disorders like vitiligo.

Low level laser therapy for Acne

LLLT seems to be to an effective treatment against acne. To fight this skin condition, blue light is often employed although red light has beneficial effects too: red light seems to increase keratinocyte turnover (like retinoids in cosmeceuticals) and reducing inflammation; blue light instead seems to regulate sebum production by reducing the activity of the sebaceous glands as well as to have an effect against Propionibacterium acnes itself, which is the bacteria responsible for acne: blue light, by being absorbed by chromophores in the bacteria, causes a photochemical reaction that induces the formation of free radicals that result in the death of the microorganism.

For visible results, once daily to 2-3 weekly sessions are advisable for at least 8-12 weeks. First results should be noticeable after 4 weeks and a maintenance protocol should be followed for sustained results over time.

Photobiomodulation therapy for Tissue healing

Chronic wounds, burns and surgical wounds seem to benefit from red light (around 630 nm) therapy due to the reduced inflammation and increased fibroblast activity and number.

For this purpose, treatment is administered every other day for 20-30 minutes.

Body contouring and localized fat reduction with low level light therapy

There is evidence suggesting the effectiveness of LLLT as a non-invasive modality for fat loss and body contouring. Moreover, LLLT has also been investigated as an adjunct to other procedures like liposuction, with the treatment administered to the area subject to surgery right before the procedure which resulted in a better cosmetic outcome, improved skin retraction and subjective improvement in the ease of performing the procedure for the surgeon.

The mechanism of action for the localized fat reduction is not yet understood.

LLLT for Scars, keloids, and hypertrophic scars

A combination treatment of both red (630 nm) and infrared (850 nm) LLLT may be beneficial to treat scars and improve their cosmetic appearance.

Complications of photobiomodulation

LLLT is a safe and non-painful treatment, cleared by the FDA and classified as a nonsignificant risk device. Patients generally don’t report any side effect or complication from this treatment and there is no downtime after it; when adverse events are reported they are mild and don’t require any medical intervention. Among the possible adverse events there are dryness of the skin, erythema, pigmentation, desquamation and itching.

You should wear eye protection. People using photosensitizing drugs or suffering from epilepsy should not perform this treatment to avoid more serious adverse events. Those with a history of skin cancer should be prudent as well: although no UV is emitted by LLLT devices, we don’t yet have enough long-term data to assess long term safety.

Controversies with LLLT

As with many other new and promising treatments, drugs, supplements, and cosmeceuticals, low level light therapy is not yet fully recognized as a treatment that works without a doubt: this is because the samples in the studies are often small, there are some methodologic flaws, they are not high quality (no double blind, sometimes the effects are evaluated with subjective parameters, etc) and they are funded by the industry making the risk of bias higher than that of independent research.

Moreover, LLLT is not as simple as flashing a light on the skin or on the area to treat. Light from a physics point of view has multiple variables such as wavelength, spatial coherence, polarity, pulse structure, fluence, and irradiance, plus there are the variables from the treatment itself like distance of application, exposure time and frequency. There is not yet a well-defined protocol to set all these parameters because we are still lacking studies comparing different settings and their clinical outcome.

Another issue with LLLT is that the manufacturers of these devices and the clinics using them to treat their patients often mention the fact that the LLLT is an FDA approved treatment: this is not true, the devices have been cleared by the FDA for safety, but the FDA did not assess the efficacy of the treatment for the proposed indications.

Laser vs led efficacy in LLLT

Much of the research available has been conducted using low powered lasers, while most of the devices found for home use or used in aesthetic clinics tend to use wide arrays of LEDs.

While LEDs have a much lower cost and allow for the treatment of large areas, from a light physics point of view they differ substantially from laser light (see paragraph above for the many variables involved, but “coherence” is one that makes some researchers argue that lasers are superior to LEDs). Nevertheless, LED LLLT already has studies showing its effectiveness and is broadly accepted: the acronym LLLT itself has been changed from low level laser therapy to low level light therapy to include any light source and not limiting it to just lasers; what is needed now is more studies comparing lasers vs LEDs for all the indications of this promising therapy, in order to understand if they are equivalent or if they differ substantially and how.

Home use devices for LLLT

The market has been inundated in the past few years by LED devices promising to rejuvenate the skin or to regrow hair among the many claims. These devices are non-clinically tested, don’t have the characteristics of medical-grade LLLT devices (such as having a lower power output) and are unlikely to produce any noticeable result.

You should always consult a dermatologist prior to performing this treatment, especially if you plan on using at-home devices: this is important to both assess if the treatment is appropriate for your specific case and to avoid missing a diagnosis and treating something very serious, like melanoma, with a led device as if it was an age spot!


Photobiomodulation is an effective therapy producing clinical results in a variety of applications. Better designed independent trials and more data are needed to avoid any controversies over efficacy of treatment and to establish detailed treatment protocols with well-defined light characteristics. The almost complete absence of risk, multiple promising indications and relatively low cost of the devices make LLLT a candidate to become one of the top treatments performed in aesthetic practices in the near future.



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